The most relevant trends in the optical networking area are the increase in the network capacity and the increase in transmission reach. A higher network capacity is obtained by increasing the channel rate and multiplexing more traffic in time domain, known as TDM (time division multiplexing), and/or by increasing the channel density, known as WDM (wavelength division multiplexing).
Advances in transmitter and receiver design, evolution of optical amplification, employment of distributed Raman amplification combined with various dispersion compensation techniques, new encoding and modulation techniques, digital wrapper technology, etc., enabled development of ultra-long reach ULR networks, where an optical signal needs to be regenerated at 3,000 km or more.
However, current WDM networks use point-to-point connectivity, where all channels are OEO (optical-to-electrical-to-optical) converted at each node. In this architecture, the advantages of the ULR cannot be fully exploited. Thus, OEO conversion at all intermediate nodes along a trail is not necessary in the majority of cases, since the modern ULR techniques allow optical signals to travel distances greater than the distanbe between two or more successive nodes without regeneration. Thus, important cost savings may be obtained by eliminating the equipment used for the unnecessary OEO conversion.
There is a need to reduce the cost of the network nodes by maximizing the distance traveled by the signals in optical format, to take advantage of the emerging ULR techniques and to provide a more efficient use of the network equipment.
There is a trend towards a new generation of optical networks, that will provide the customers with the ability to automatically establish an end-to-end connection at a push of a button. This new architecture has, among numerous other advantages, the ability to treat each connection differently, so as to provide the respective user with an individualized class of service, with the corresponding revenue differentiation. End-to-end connection granularity means that the nodes of the network need to be able to switch the connection in optical format, while automatically regenerating the signal only when necessary. This approach dramatically reduces the node complexity, and consequently the network cost.
Automatic switching and regeneration result in regenerators and wavelengths becoming two of the most important resources of the photonic networks. In general, they could be allocated to a connection according to certain rules, which are mostly dictated by the class of service for the respective connection, and by the particular architecture of the network. Methods to economically use these resources and minimize blocking of new connection requests are crucial to cost reduction and operational efficiency of photonic networks.
Determination of the number of regenerators and their nodal allocations is one aspect of efficient resource management in photonic networks. Regenerators need to be switched into an end-to-end connection so that the signal is regenerated and restored to superior quality before propagation and transmission impairments corrupt the signal entirely.
Further, in switched optical networks, the selection and assignment of the right wavelength to each optical path for the best possible utilization of available wavelengths depends on several factors. These factors include (a) maintaining a current view of the current network connectivity; and (b) since “not all wavelengths are equal”, providing the network with the knowledge of the individual wavelength performance.
Knowing the current wavelength allocation allows the network to select one or more unused wavelengths to serve a new connection. This is even more important having in view that this allocation is dynamic, the connections being set-up and removed by users at arbitrary moments. Knowing the individual performance of all wavelength available in the network and the pertinent topology information (fiber type, link loading, etc), allows matching a wavelength to an optical path, which allows further reduction of the network costs.
Nonetheless, the selection and assignment of the right wavelength for each optical path for the best possible utilization of available wavelengths is a complex problem. A meaningful solution to this complex problem is needed to facilitate the best possible use of wavelengths as a resource while satisfying connection setup demands.